Engine support means that the compiler or more simply, as the words state, that the engine on it can run, this has on the first base nothing to do with games
You also dont need be technological about it, its common sense. If your logic worked, you basicly saying something like this: My patato PC can run Unreal Engine 4 Games, for example The Vanishing of Ethan Carter, which is a (very good) walking simulator, so it must also run eve valkyrie with more then 10 fps per second (sadly it cant). A Engine does not magicly change processing power
So no this has nothing to do with "excuses" of third partys, which are still legit when it comes to porting.
but still its nice that its supported tho, more oppurtintys and less hassle for devs